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Chaps

I have the 'orrible feeling I know the answer to this, but here goes...

In his infinite wisdom, a PO changed the brake fluid to DOT 5 silicon and, while the '6 was in for a service last week, the brakes were adjusted.  I only occurred to me yesterday that the fluid must have been topped up and I'd forgotten to underline (again) that only the silicon stuff was to be used, so I checked with the guy.  Yes, he'd topped up a bit.  He'd used oh, um, not DOT 5.1, maybe DOT 4... definitely 'Racing' grade, 'cause it's the only stuff he uses... um.

So, I have maybe 30-50cm3 of the mineral stuff sitting in my silicon system.  Sheet.

I know that the proper job is to empty the system, flush it with meths, let it dry for several days and replenish with the accursed silicon, but...

-  can the mineral can be scooped off the top of the master cylinder reservoir or does it have a greater SG and is already coursing its way to the brake seals?

-  alternatively, can I risk a small addition of mineral without there being adverse effect?

-  is there a risk of sudden seal failure in the meantime?

Advice much appreciated.

Paul

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There is much on the net about this.  Most is speculation, bollocks and twaddle as far as I can tell.  Do you definitely have DOT 5 silicone  in the system (usually purplish, though fades to yellow over time) and not DOT 5.1 which (confusingly) is polyglycol based and more or less compatible with DOT 3 & 4?  Does your M/C not have a dirty great warning label tied round it's neck?  Needs one.....

Seals:  As the same seals are used for both fluid types I can see no reason why there should be any risk of seal failure.

The two fluid types don't readily mix - some say they remain separate, others that they form a gel - both may be true with the gel forming over time or when forced to mix.

The SG of the polyglycols is higher than silicone.  Not the best news in your case as it means that the addition is now most likely at the bottom of the master cylinder rather than sitting on the top......  I'd still be tempted to get a big syringe and draw out what is in the the master cylinder - careful observation may give some clues as to the extent of the problem....  Beyond that, if only driven a short distance possibly just removing and cleaning out the M/C would catch all the contaminant - you'd still need to re-bleed, though possibly only the nearest corner if lucky.

I dislike silicone fluid - and this is one reason why.  No silicone allowed on the estate!

Nick

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Nick

Many thanks for this - hugely helpful.  Unfortunately, I've driven a good 200 miles since the service (I am finding that the delay in epiphanies increases with age), so I anticipate that a good deal of mixing has taken place.

I have the container from the last time the system was flushed and re-filled and it is definitely DOT 5, but the fluid is completely transparent.  This is a repetition of a cock-up with a previous mechanic, who knew about the silicone (I can still recall his beaming face as he announced, "I've gone one better and filled the system with DOT 5.1")  On that occasion, I learnt of the difference between DOT 5 and 5.1 only when I discovered that the rear wheels were both sitting in little puddles of brake fluid a good two weeks after the mechanical intervention and the shoes and drums were so contaminated that they were toast.  Quite why the seals failed I now do not know.

Just to summarise, I assume that the best belt'n'braces approach is to bleed the whole system out and replenish with the damned silicone stuff, yes?

Cheers

Paul

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Not sure that very much mixing will have occurred beyond the master cylinder as there really isn't very much displacement happening in a healthy braking system.  Perhaps I'm over-optimistic...... no direct experience.

Were I in this position and feeling moved to go beyond cleaning out the M/C I think I would first bleed through the "shortest leg" (that's the shortest pipe-run) by disconnecting the flexi hose from the caliper and running enough fresh fluid through to clear the contamination before reconnecting the caliper and bleeding normally.  I say this as in your situation I think it most unlikely that the contaminated fluid will have reached the calipers yet and I'd prefer to avoid intentionally sending it there.

I would then bleed the other three corners generously and watch for sighs of contamination (though I'd be surprised if there were more than very minor signs).  Much better to use a pressure-bleeding system if at all possible as allows continuous flow (less chance of pockets of contamination lingering in vertical bends) and doesn't hammer the M/C.

Presumably your mechanic isn't offering to resolve the situation......?

Nick

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Thanks again, Nick

My mechanic?  A rotund, cheery chap, who is doing a very convincing imitation of Mr Teflon.  "Nothing to be worried about, everything is fine," he beamed this morning.  He wasn't sure which specification he poured into the MC, but he was gushing in his assurances that it was only good stuff that went in, no rubbish.

I'll follow your advice and empty the MC, re-fill it with fresh DOT 5 and bleed from the FLH wheel, being the nearest.

Cheers

Paul

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Ok.  I'd probably draw off as much as possible from the M/C reservoir as possible first before commencing the flushing/bleeding process.  Might be interesting to dump that into a glass jar, allow to stand, and see if a separation layer forms?  Any rate, the less of the wrong stuff that gets into the system proper, the better.

Nick

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Is bleeding such a chore?   I just replaced my main line from M/C to T-piece, as it was leaking from the connection at the M/c.   I think the flange formed on the tube end had got squashed.   Replaced with Aeroquip, so much easier to run across a bulkhead loaded with other bits and pieces.

Anyhoo, started at the back right, BIG bubbles then none to my Halfords single handed bleeder.  Do the others in order, done in half an hour.

John

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Paul,

 

I had cause to speak to a Girling engineer about a problem, and flushing came up an I said the same " I know that the proper job is to empty the system, flush it with meths, " and his response was on no account use meths on brake systems as it is mineral oil based and will damage the seals. so I didn't.

The silicone i use from Automec says on the package that it will mix with dot 4 type fluids but any advantage will be lost.

Alec

 

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Girling engineer should know better. 

Meths is methylated spirit.  Mostly ethanol with some methanol added to stop you drinking it.  NOT mineral oil based.  EPDM, the elastomer used for braking system seals, is also resistant to ethanol and methanol.

Nick

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Hello Nick,

 

I'm no chemist so I heeded his advice?  He did sort out the problem I had though.

Incidentally I don't think the addition of methanol stops some people :-)

 

Alec

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1 hour ago, 2.5piman said:

Incidentally I don't think the addition of methanol stops some people :-)

This is true.  They don't last long though.  Ruins your kidneys and makes you blind.

Nick

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35 minutes ago, Nick Jones said:

This is true.  They don't last long though.  Ruins your kidneys and makes you blind.

Nick

Hello All

              I was told to mix it with milk!

Roger 

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Ive been on a job when people have drunk 100% spirits & diluted it with orange juice, one bloke woke up & could only see in black & white for 3 days, lucky he didn't go blind, was a close thing.

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11 hours ago, RedRooster said:

Ive been on a job when people have drunk 100% spirits & diluted it with orange juice, one bloke woke up & could only see in black & white for 3 days, lucky he didn't go blind, was a close thing.

Hello All

             Toooo much orange juice!

Roger

Edited by rogerguzzi

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This is probably a bit late for you Paul, but here it is anyway.

  -  As posted above, SG is different, so the mineral oil will sink to the bottom.

  -  The two types of fluid don't easily mix (maybe they will with time / shaking / centrifuge....).

  -  There may be a tendency for the seals to swell slightly differently with the 'other' fluid.  This is why there can be leaks.  This will be a long term effect (months).

  -  Bleed through plenty of fresh fluid and don't worry about it.

 

Cheers,      Will.

 

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..... I had reason the other day to use a syringe to reverse bleed a go kart system.  It worked fantastically.  The large volume positive displacement of the (100 ml) syringe purged all the air from the system.  Simply open the bleed nipple with the syringe attached, and push the fluid backwards.  Of course you need to keep emptying the master cylinder.......

It's very satisfying watching the bubbles come through into the master cylinder reservoir....

I think the problem on many bikes / go karts is that the displacement of the master cylinder is too small to push anything through.

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.... arrrrh, that reminds me.  I need to bleed the brakes on my son's bicycle.  Lots online about this but the system is stated as using a mineral fluid, so I was going to use normal automotive DoT 4 or DoT 5.1 - rather than buying expensive bike specific stuff.

What do you all think......?

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Thanks, Will

I finally got round to whipping the cap off the MC this morning and, interestingly, the clear mineral stuff was at the top of the reservoir and there was still some purple stuff around the outlet at the bottom. I sampled both with a syringe for certainty and the clear stuff mixed fully with water, whilst the purple stuff separated at the top.

So, I syphoned off the mineral fluid, pulled on my glad rags to head out to the local equivalent of Halfords... then remembered that today is Sunday and the law changed to forbid Sunday trading a couple of months ago.

So, I will get a litre of the accursed silicone tomorrow, top up the reservoir and have my jolly rotund mechanic bleed it thoroughly because (i) I won't have time to do it myself this week, (ii) the bugger should have spotted that the MC had purple fluid to start with and (iii) there is a large DOT 5 ONLY warning tag attached to the pipework below the MC.

One remaining question: the MC reservoir appears to be split in two, with the smaller part barely accessible from the neck once the cap is removed. Is this a reserve tank or a balancer? I can't see any way in which the levels might equalise...

Thanks

Paul

 

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... a litre. Sheet, this stuff ain't cheap.

Any guesses on the capacity + reasonable bleed for a TR6 brake system?

Paul

 

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A litre will be fine, I only used about 0.5 litre when filling the Vitesse and that included a fair amount of gratuitous flushing just to be sure! 

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Agreed that a litre is ample.  500mls probably plenty.

Re. the separate compartments, does this car have dual circuit brakes?  If so, it is to stop one leaky circuit completely draining the system - which would defeat the point of having dual circuits!

Nick

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Ah, dual circuit brakes... didn't think of that...
Thanks again, Nick.  Odd, however, that the reservoirs are asymmetric and the smaller one barely accessible.

Paul

 

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